(1) Field of Invention
The present invention relates to a limited slip differential mechanism for an automotive vehicle and a method for making the same, and more particularly, to a method of developing a limited slip differential having a side gear clutch pack by use of a cold forming process.
(2) Background of the Invetion
Automotive vehicles include differential assemblies to transmit torque from a transmission output shaft to axle shafts, which allow the right and left driven wheels of the vehicle to rotate at different speeds. One type of differential assembly or mechanism is commonly referred to as a bevel gear differential, and is one of the most frequently used differentials due to its relatively simple and effective design.
Bevel gear differentials typically include two or four pinion gears, depending upon the weight of the vehicle and the magnitude of torque transmitted by the powertrain. The pinions, are supported together with two side bevel gears in a differential housing, which is formed as a one piece iron casting. Some differentials, commonly referred to as limited slip differentials, further include side gear clutch packs, which are disposed within the differential and which are designed to improve the performance of the differential. Particularly, the clutch packs allow the differentials to provide more driving force to a wheel with traction if the opposing wheel loses traction or begins to spin. In this manner, limited slip differentials are used within sports cars for increased traction while cornering and within off-road vehicles where the drive wheels often lose traction.
The clutch plates within these prior limited slip differentials are retained to the differential housing by use of two integrally formed tabs or xe2x80x9cearsxe2x80x9d that mate with the inner surface of the differential housing pocket. The differential housing is typically constructed from a cast iron metal, and the pocket that houses the ears is machined for accuracy or is left xe2x80x9cas-castxe2x80x9d, and does not retain its dimensional characteristic after extended use. Over time, backlash may result, creating the possibility of noise and reduced performance. Additionally, the clutch packs are limited in size due to the housing wall thickness required by the casting process and the stiffness requirements of the housing. These size constraints undesirably limit the torque capacity of the clutch packs.
Another drawback related to these prior cast differentials is that they have significantly lower ductility and yield strength relative to most steel. Thus, the cast differential housings must typically be formed with relatively thick walls to provide supplemental strength. The greater thickness of the walls produces increased weight and increased inertia that reduces powertrain efficiencies. Also, the cast iron properties of the housing require the outer ring or bevel gear of the differential to be mounted on with several bolts, thereby increasing machining and assembly costs. Furthermore, due to limitations of the machining process and the assembly of the gears within the prior differentials, one-piece cast housings are typically only limited to two pinion gear designs which limits torque capacity.
The manufacturing and machining of these one-piece cast housings further provides additional drawbacks. For example and without limitation, iron castings require offsets to compensate for shrinkage, and thus, many turning or milling operations are necessary to achieve dimensional accuracy during machining. Also, assembly of these prior differentials can typically only be performed manually due to the number of different joining axes. The required machining processes further cause excessive tool wear, and require expensive and space-intensive transfer lines with low flexibility.
There is therefore a need for a new limited slip differential mechanism and a method of manufacturing the same, which utilizes a cold forming process, and which provides for improved performance, a modular design, reduced weight and size, and decreased manufacturing cost and complexity.
A first non-limiting advantage of the present invention is that it provides a limited slip differential mechanism which is made by use of a cold forming process and which overcomes the drawbacks of prior systems.
A second non-limiting advantage of the present invention is that it provides a method for forming a housing for a limited slip differential which has a reduced wall thickness, thereby allowing for a larger clutch pack and/or a clutch pack with fewer plates to be utilized within the housing.
A third non-limiting advantage of the present invention is that it simplifies and reduces the cost of the differential assembly, relative to prior differential assemblies, by simplifying the manufacturing process and by eliminating pinion retaining bolts, snap rings, and other components.
A fourth non-limiting advantage of the present invention is that it provides an enclosed transfer case design with improved stiffness relative to prior cast designs, and an enclosed pinion which eliminates the need for clips and lock screws.
A fifth non-limiting advantage of the present invention is that it allows for automated assembly, thereby simplifying the assembly procedure and reducing cost.
A sixth non-limiting advantage of the present invention is that it reduces material cost and eases manufacturing by using chipless forming operations.
A seventh non-limiting advantage of the present invention is that it allows for an encapsulated pinion shaft, and further allows for use of two, three, or four pinion gear combinations for improved torque capacity.
According to a first aspect of the present invention, a limited slip differential assembly is provided. The assembly includes a first housing portion having a first splined inner surface; a second housing portion having a second splined inner surface, the second housing portion being coupled to the first housing portion and cooperating with the first housing portion to form a cavity; a differential mechanism disposed within the cavity and including a pinion shaft, pinions which are coupled to the pinion shaft, a first gear member in meshing engagement with a first of the pinions, and a second gear member in meshing engagement with a second of the pinions; a first side clutch pack including a plurality of first clutch plates having a first splined outer surface which is coupled to the first splined inner surface, and a plurality of second clutch plates which are coupled to the first gear member; and a second side clutch pack including a plurality of third clutch plates having a second splined outer surface which is coupled to the second splined inner surface, and a plurality of fourth clutch plates which are coupled to the second gear member.
According to a second aspect of the present invention, a method is provided for forming a housing for a limited slip differential mechanism. The method includes the steps of forming a first housing portion having a first splined inner surface; and forming a second housing portion having a second splined inner surface, the first and second splined inner surfaces being effective to respectively mate with and operatively retain a plurality of first and second clutch plates.
These and other objects, aspects, features, and advantages of the present invention will become apparent from a consideration of the following specification and the attached drawings.